Stratigraphy of Quaternary Dunes by Sand Mineralogy and Pedogenic ...
STRATIGRAPHY OF QUATERNARY DUNES BY SAND MINERALOGY AND PEDOGENIC FEATURES, LOS OSOS, CALIFORNIA
A Thesis presented to the Faculty of California Polytechnic State University, San Luis Obispo
In Partial Fulfillment of the Requirements for the Degree Master of Science in Agriculture, Specialization in Soil Science
by Lyssa A. Cousineau June 2012
© 2012 Lyssa Anne Cousineau ALL RIGHTS RESERVED
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COMMITTEE MEMBERSHIP
TITLE:
Stratigraphy of Quaternary Dunes by Sand Mineralogy and Pedogenic Features, Los Osos, California
AUTHOR:
Lyssa A. Cousineau
DATE SUBMITTED:
June 2012
COMMITTEE CHAIR:
Dr. Lynn E. Moody, Professor of Natural Resources Management and Environmental Sciences
COMMITTEE MEMBER:
Dr. Antonio F. Garcia, Professor of Geology in the Physics Department
COMMITTEE MEMBER:
Dr. William L. Preston, Professor of Geography
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ABSTRACT Stratigraphy of Quaternary Dunes by Sand Mineralogy and Pedogenic Features, Los Osos, California Lyssa A. Cousineau The goal of this study was to assess mineralogy and pedogenic features of sand dunes in a stratigraphic sequence. The purpose was to determine whether these features significantly differ to reflect age differences with depth within the sequence. This study was conducted in Montaña de Oro State Park, located on the central Californian coast eighteen kilometers northwest of San Luis Obispo in San Luis Obispo County. Samples were collected from the vertical exposure of one dune face by stratified random sampling at 1.0-m vertical intervals. Particle size distribution was determined through particle-size analysis by hydrometer and sieve. Electrical conductivity and pH were determined using a 1:1 soil/water paste. Total soil carbon and nitrogen contents were determined by combustion. Pedogenic iron oxides were extracted by ammonium oxalate in the dark and citrate-bicarbonate-dithionite, and then quantified by flame atomic absorption spectrometry. Sand mineralogy of fifteen thin sections was analyzed by polarized light microscopy. Grain counts quantified the sand mineralogy of the thin sections. Total carbon significantly decreases with soil depth and age reflecting modern development of soil at 0 to 1 meters within the stratigraphic sequence. Certain morphologic and mineralogic features, including an increase in nitrogen content and the presence of fossilized fungal hyphae, suggest that a buried A horizon may be preserved 9 to 10 meters below the crest of the modern dune complex. Using relative dates compiled from previous research, it was determined that the soil at 9 to 10 meters depth was developed 15-ka to 30-ka after sand deposition during a eustatic sea level lowstand. The presence of fossils in general suggests that the ancient soil was rapidly covered.
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ACKNOWLEDGEMENTS There are so many individuals to thank for this accomplishment, I cannot mention them all. Therefore, I provide this broad (and sincere!) statement. To my colleagues from the Natural Resources Management and Environmental Sciences Department as well as my family and friends spread throughout North America, thank you for teaching me, encouraging me, and allowing me to laugh at myself when the going got rough. I extend sincerest gratitude to my committee chair, Dr. Lynn Moody. Thank you for your wisdom, guidance and continual support. You are an inspiration and a joy to be around, Lynn, and I would not have grown by leaps and bounds in two years without your counsel. You will be missed in the soils profession when you retire this year. I would also like to thank my graduate committee, Dr. William Preston and Dr. Antonio Garcia. Thank you for your manuscript edits, insights, and humor inside and outside of committee meetings. Laboratory assistance was absolutely essential to my research. Technician Craig Stubler, your expertise was invaluable to my laboratory procedures and analysis. Thank you for your dedication in helping me with my thesis. You went above and beyond what I asked for, and without hesitation. All departments should be so blessed to have a technician such as you. Adrian Gallo and Scott Pensky, my undergraduate research assistants, thank you for your long hours in the lab. You kept the lab lively when I needed it most, and provided me with a fresh outlook on my research. Thomas Witman, Craig’s lab assistant, surprised me by volunteering his time in the lab working on my project. Without you guys, I would not have finished in such a timely manner. I hope this experience has been as great a learning tool for you as it has been for me. I look forward to hearing about your adventures in soil science when you begin your careers in the near future. Dr. Tryg Lundquist, from the Civil and Environmental Engineering Department at Cal Poly San Luis Obispo, thank you for letting me use your centrifuge for sample preparation. We ended up completely wearing out a relay on your thirty-year-old machine, and I had to completely redesign my procedure because the centrifuge is now unavailable indefinitely. Whoops. National Petrographic Service, Inc. prepared thin sections with a partial grant from the Natural Resources Management and Environmental Sciences Department at Cal Poly San Luis Obispo. To Lisa Wallravin, Melanie Gutierrez and Becky Powell: You work tirelessly behind-the-scenes to make sure all the coursework, paperwork, and formatting is correct. Without your dedication and hard work, none of the Master’s students would ever make it out of Cal Poly! Jacqueline Tilligkeit, Dr. Thomas J. Rice, Lynette Niebrugge, Leslie Wilson, Shelby Delfino, and Brittany Piarulli, thanks for all of your encouragement and support in completing this thesis. I am particularly grateful to Donovan Hall, who not only assisted me with sample collection, but also was my chauffer, encouragement, chef, best friend, shoulder to cry on, and (amazingly) my occasional lab assistant. When I started this thesis, I had yet to meet you; now I cannot imagine my life without you. Last but not least, I would like to thank my parents and the Lord; without you, I would have never made it this far.
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TABLE OF CONTENTS Page LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix INTRODUCTION .............................................................................................................. 1 Geologic Background ............................................................................................. 2 Marine Terraces ...................................................................................................... 4 Relative Ages .............................................................................................. 5 Basal Dune Chronology .............................................................................. 6 Sand Dune Development ........................................................................................ 7 Lamellae ...................................................................................................... 8 Anthropogenic Activity .......................................................................................... 9 MATERIALS AND METHODS ...................................................................................... 11 Study Area ............................................................................................................ 11 Climate ...................................................................................................... 11 Vegetation ................................................................................................. 11 Soils........................................................................................................... 12 Methods................................................................................................................. 13 Sample Collection ..................................................................................... 13 Laboratory Analyses ................................................................................. 15
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Statistical Analyses ................................................................................... 16 RESULTS ......................................................................................................................... 18 Chemical Features ................................................................................................. 18 Texture .................................................................................................................. 22 Particle Size Distribution .......................................................................... 22 Roundness and Sorting ............................................................................. 24 Mineralogy and Micromorphology ....................................................................... 25 Selective Dissolution ............................................................................................ 31 DISCUSSION ................................................................................................................... 36 Modern Soil Development .................................................................................... 36 Lamellae .................................................................................................... 36 Pedogenic Iron Oxides .......................................................................................... 37 Paleosol ................................................................................................................. 37 Relative Dating of Paleosol .................................................................................. 39 CONCLUSIONS............................................................................................................... 41 LIST OF REFERENCES .................................................................................................. 43 APPENDIX ....................................................................................................................... 49 A.
Table of Results for Regression Analyses .............................................. 50
B.
Plates of Thin Section Features ............................................................... 53
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LIST OF TABLES Page Table 1-1. The four major coastal dune phases of stabilization and their maximum ages in the Morro Dune Complex (Orme, 1990). ..............................................7 Table 3-1. Selected chemical features of stratigraphic sequence. .....................................19 Table 3-2. Particle size distribution of sand grains. ...........................................................23 Table 3-3. Prominent sorting and roundness of sand grains. Roundness not determined at 5 to 6 meters because thin sections were not produced for that stratigraphic interval. ...........................................................................25 Table 3-4. Sand mineralogy of thin sections. All samples were averaged except for 0 to 1 meters, which is a single sample set because of sample loss. ..........26 Table 3-5. Root counts in thin sections. Total root count includes roots and root channels discovered independent of the grain count. ......................................29 Table 3-6. Selective dissolution chemical data for stratigraphic sequence. ......................33 Table 3-7. Grouping information using the Tukey method with 95% confidence for total pedogenic iron oxides (Fed) and poorly crystalline iron oxides (Feo)..................................................................................................................34
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LIST OF FIGURES Page Figure 1-1. Late Quaternary sand dunes of the Morro Dune Complex in Estero Bay. Active dunes are adjacent to the coast, and younger parabolic dunes reside east of the active dunes. Morro barrier tip circled in red. Figure adopted from Orme, 1990. ....................................................................3 Figure 1-2. Timeline of geologic, glacial, and historic events pertinent to the central Californian coast. ..................................................................................5 Figure 1-3. Lamellae are prominent in the stratigraphic sequence studied (Photo credit: Lyssa A. Cousineau). ............................................................................9 Figure 2-1. Oblique aerial view of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Copyright © 20022012 Kenneth & Gabrielle Adelman, California Coastal Records Project, www.Californiacoastline.org). The specific site of study is outlined and enlarged. ....................................................................................12 Figure 2-2. View from beach of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Lyssa A. Cousineau). Donovan Hall, who is 1.73m tall, is shown for scale. ....................................14 Figure 2-3. Sampling intervals depicted on oblique aerial view of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Copyright © 2002-2012 Kenneth & Gabrielle Adelman, California Coastal Records Project, www.Californiacoastline.org). ..............15
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Figure 3-1. Average pH of stratigraphic sequence. Depth is in meters and error bars display standard error. ............................................................................20 Figure 3-2. Average total carbon of stratigraphic sequence. The trend line displays exponential regression. Depth is in meters and error bars display standard error. .................................................................................................20 Figure 3-3. Average nitrogen of stratigraphic sequence. Depth is in meters and error bars display standard error. ....................................................................21 Figure 3-4. Electrical conductivity of stratigraphic sequence. Depth is in meters and error bars display standard error. .............................................................21 Figure 3-5. Sand distribution as determined by particle size analysis in stratigraphic sequence. Depth is in meters and error bars display standard error. .................................................................................................23 Figure 3-6. Silt and clay distribution as determined by particle size analysis in stratigraphic sequence. Depth is in meters and error bars display standard error. .................................................................................................24 Figure 3-7. Sand mineralogy of stratigraphic sequence. Depth is in meters, error bars display standard error, and x-axis is in percent. .....................................27 Figure 3-8. Selected sand mineralogy of quartz in stratigraphic sequence. Depth is in meters, error bars display standard error, and x-axis is in percent. ............27 Figure 3-9. Selected sand mineralogy of plagioclase in stratigraphic sequence. Depth is in meters, error bars display standard error, and x-axis is in percent. ...........................................................................................................28
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Figure 3-10. Quartz to plagioclase ratio in stratigraphic sequence. Depth is in meters and error bars display standard error. .................................................28 Figure 3-11. Selected sand mineralogy of minor grains in stratigraphic sequence. Depth is in meters, error bars display standard error, and x-axis is in percent. Quartz and plagioclase omitted from this figure to better depict concentrations of minor grains. ...........................................................29 Figure 3-12. Cross section of root covered by mycorrhizal sheath (FitzPatrick, 1993) located 0 to 1 meters depth under cross-polars at 40X magnification (Photomicrograph credit: Lyssa A. Cousineau). .....................30 Figure 3-13. Filamentous, branching structures of fungal hyphae between grains located 9 to 10 meters depth under plane polarized light at 40X magnification (Photomicrograph credits: Lyssa A. Cousineau and Adrian Gallo). .................................................................................................31 Figure 3-14. Poorly crystalline iron oxides (Feo) of stratigraphic sequence. Depth is in meters and error bars display standard error. .........................................33 Figure 3-15. Total pedogenic iron oxides (Fed) of stratigraphic sequence. Depth is in meters and error bars display standard error. .............................................34 Figure 3-16. Ratio of poorly crystalline iron oxides (Feo) to total pedogenic iron oxides (Fed) of stratigraphic sequence. Depth is in meters and error bars display standard error. ............................................................................35
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INTRODUCTION Dune geomorphology and coastal dune research are important because coastal dunes are dynamic. Coastal dunes experience periods of stabilization and inconstancy, and are subject to frequent and rapid changes due to sea level flux, shifts in vegetation, and anthropogenic activity (Carter et al., 1990; Orme, 1990 and 2005). These changes are compounded by modern global climate change, which is also altering coastal environments on a global scale. A lack of complete understanding of coastal dunes during this period of rapidly evolving landscapes may lead to the loss of these habitats for future generations. Preservation is crucial for archaeological research. The value of archaeological sites is dependent on accurate provenance, or the age and location of artifacts. If archaeologists understand dune development and age, they will be afforded with a better opportunity to determine artifact provenance. Shell middens and archaeological sites created by the Chumash at Montaña de Oro State Park (CA State Parks, 1988; Orme, 1990 and 2005) are often associated to the dunes. Understanding of Chumash life ways will be enhanced by this research. The general public enjoys the central coast of California because of good weather, opportunities for recreational activities, and a plethora of native fauna and flora. These qualities have also been valuable to the Chumash for thousands of years. It is our job to preserve this heritage. Several studies have analyzed the development of sand dunes, sandy soils, and underlying marine terraces (Aniku and Singer, 1990; Graham and O’Geen, 2010; Johnson et al., 2008; Little et al., 1978; Macphail and McAvoy, 2008; Miles and Franzmeier, 1981; Moody and Graham, 1995 and 1997; Reheis et al., 2005; Sauer et al.,
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2010; Tsai et al., 2007; Tsai et al., 2010; Wagner et al., 2007), but characteristics of coastal dunes worldwide are still being compiled. This study analyzes stratigraphy of a select dune complex located within Montaña de Oro State Park. The goal of this study is to assess mineralogy and pedogenic features of sand dunes in a stratigraphic interval. The purpose is to determine whether these features significantly differ to reflect age differences with depth. Geologic Background Tectonic activity, sea level changes, and anthropogenic events are paramount to the evolution of the central California coast (Keller, 1992; Orme, 1990 and 2005). Montaña de Oro State Park is at the northwest end of the San Luis Range. This range, along with the Santa Lucia and Casmalia Hills Coastal Ranges developed over the last 5 to 3.5 million years due to folding and faulting along the Pacific and North American plates (Page et al., 1998). More recently, the Morro Bay estuary began to form approximately 5-ka (Page et al., 1998). The current modern-day landscape of the Morro Bay estuary developed when an oceanic breach flooded a structurally unsound trough (Figure 1-1; CA State Parks, 1988; Orme, 1990 and 2005). Orme (1990) named the dune deposits in this area as the Morro Dune Complex. The Morro Dune Complex has been the focus of study since the turn of the twentieth century. Marine terraces between Morro Bay and Santa Maria Valley were first noted by Fairbanks (1904). Fairbanks classified the rock sequence of Montaña de Oro as Monterey Shale (i.e., Monterey Formation). But this delineation was overturned by Hall (1973) who reclassified the shale, siltstone, and claystone as part of the Miguelito
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Member of the Pismo Formation (Keller, 1992; Orme, 1990). Later studies conducted by Pacific Gas and Electric Company (1973, 1988) and Cleveland (1978) followed Hall’s classification.
Figure 1-1. Late Quaternary sand dunes of the Morro Dune Complex in Estero Bay. Active dunes are adjacent to the coast, and younger parabolic dunes reside east of the active dunes. Morro barrier tip circled in red. Figure adopted from Orme, 1990. 3
Marine Terraces Marine terraces develop due to oscillating eustatic sea level highstands and lowstands. During an interglacial period, when less water is bound in glacial ice, sea levels rise. Periods of global sea level rise are known as transgressions, and periods of global sea level fall are termed regressions. Wave erosion from elevated sea level cuts a bedrock bench at the shoreline and thus creates a sea cliff that adjoins perpendicular to a modern wave-cut platform at the shoreline angle. These features are later uplifted by tectonic forces. The uplifted wave-cut platform is now a called a strath and the former (uplifted) sea cliff is now termed a riser. As the shoreline ridge and platform continues to uplift and waves from the modern sea level cut into the bedrock bench, additional straths and risers are formed and a staircase of shoreline platforms emerges. The top of the staircase is inhabited by the oldest shoreline platforms; the straths and risers become progressively older inland and with increasing elevation. The modern wave-cut platform overlain by the current coastal shore is generally indicative of the most recent coastal activity. However, sea level regressions can create platforms which later exist under water during a eustatic sea level highstand or interglacial period. Orme (1990) identified intermittent uplift of shoreline ridges in the Morro Dune Complex since about 100-ka (Figure 1-2). The current average uplift rate for marine terraces located between Islay Creek and Hazard Canyon in Montaña de Oro State Park, which is very close to the study site, is approximately 0.24 m/ka (Hanson et al., 1994). During eustatic sea level lowstands, sediments previously below sea level become subject to eolian processes. Winds dominantly from the west (CA State Parks, 1988; Orme, 1990) transport sand dunes inland to cover the wave-cut platforms. These dunes
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are migratory and are constantly being reworked by the winds, but coastal shrubs and vegetation create stationary areas within otherwise mobile modern sand dunes.
Figure 1-2. Timeline of geologic, glacial, and historic events pertinent to the central Californian coast. 1 Relative Ages Dates of the marine terraces at Morro Bay and Montaña de Oro State Park have been disputed over the years. Using a combination of amino acid racemization, uraniumseries dating from coral and vertebrate bone samples, invertebrate faunal assemblages, 1
(Ogg, 2010) 2(Muhs, 2012) 3(Gibbard and Kolfschoten, 2004) 4(Orme, 1990) 5(CA Dept. of Water Resources, 2002) 6(Moody and Graham, 1995) 7(Jack Meyer, Far Western Anthropological Research Group, Inc., personal communication, 2012) 8(Hanson et al., 1994) 9(Bischoff and Rosenbauer, 1981)
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and comparisons of terrace elevation with altitudes of previously-dated terraces, Hanson et al. (1994) determined that an array of twelve elevated, essentially flat-lying marine terraces exist in the San Luis Range between Morro Bay and the northern boundary of Santa Maria Valley. According to this study, the youngest and lowest two terraces of the dozen correlate consecutively with sea-level transgressions at 80-ka and 120-ka. Hanson et al. (1994) concluded that a thin terrace dating to the 105-ka transgression was eroded and subsequently not preserved. A concurrent study by Moody and Graham (1995) determined that the lowest terrace dates to the 120-ka interglacial, and that overlying sands were first deposited during the Pleistocene (12-ka to 27-ka or 48-ka) and reworked later during the Holocene (1-ka). Basal Dune Chronology Modern beaches and dune fields, which date from the late Pleistocene to the early Holocene, overlie the marine terraces in Morro Bay and at Montaña de Oro State Park (Hanson et al., 1994; Orme, 1990 and 2005). Sands of these beaches and dune fields were deposited on the San Luis Range during the last eustatic sea level lowstand at about 15-ka (CA State Parks, 1988; Orme, 1990 and 2005). Dates from Gibson (1981) and Orme (1990) indicate that the surface dune deposits located 2.3 km south of the Morro barrier tip (see Figure 1-1) date between 3568 and 3830 BP (before present) (Jack Meyer from Far Western Anthropological Research Group, Inc., personal communication, 2012). The study site is located relatively close to the surface dune deposits dated. Therefore, surface dune deposits of the study site likely correlate with these ages. Additional radiocarbon
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dating of buried soils indicates that dunes which were formed during the last drop in sea level have since partially eroded (Orme, 1990). Orme (1990) defined four major phases of dune stabilization in Morro Bay (Table 1). His work suggests that the modern dunes of the Morro Dune Complex are experiencing a period of instability, and that dune erosion is marked and rapid in the region today. It is likely that the basal layer of the study site corresponds with the youngest paleodunes which were deposited on the San Luis Range between 15-ka to 30ka (CA State Parks, 1988; Orme, 1990 and 2005). Table 1-1. The four major coastal dune phases of stabilization and their maximum ages in the Morro Dune Complex (Orme, 1990). Phase
Expression
Maximum age (uncalibrated)
Holocene III
Active dunes
< 200 BP
Holocene II
Younger parabolic and lobate dunes
< 1,730 BP
Holocene I
Older parabolic dunes
≤ 4,160 BP
Late Pleistocene
Youngest paleodunes
< 27,000 BP
Sand Dune Development Coastal watersheds brought inland sediment to the coasts by flood events, which were then reworked by waves, winds, and currents to form the modern sand dunes found along the Pacific coast. The collection of sediment on these coasts was most prevalent during the wetter climate of the Pleistocene. However, tectonic deformation of Los Osos Valley toward the end of the Pleistocene limited sediment delivery (Orme, 2005). Dunes are influenced by beach profile characteristics, wind regimes, and sediment grain size distribution (Carter et al., 1990). Sand deposits, which make up coastal dunes, are positioned in response to obstructions including vegetation and anthropogenic 7
obstacles such as jetties and buildings. The wave-cut platforms at Montaña de Oro State Park are overlain with a thin (1 to 2 m) deposit of gravel and marine sand, and a thick (up to 30 m) deposit of eolian sand, alluvium, and colluvium (Hanson et al., 1994; Moody and Graham, 1997; Orme, 1990). Lamellae The dune complex for this study contains an extensive array of lamellae throughout the soil section (Figure 1-3). The Keys to Soil Taxonomy, Eleventh Edition (NRCS, 2010) defines lamellae as the following: A lamella is an illuvial horizon less than 7.5 cm thick formed in unconsolidated regolith more than 50 cm thick. Each lamella contains an accumulation of oriented silicate clay on or bridging the sand and silt grains (and rock fragments if any are present). Each lamella is required to have more silicate clay than the overlying eluvial horizon. In general, lamellae number, color, and thickness increase with pedogenic development (Schaetzl, 2001). Specifically, to some threshold depth below which clay illuviation is negligible, the process of lamellae development increases with depth and age of a soil sequence. This is because lamellae migrate downward in a soil sequence. The clay content moves from upper to lower lamellae during development (Soil Survey Staff, 1999). Because of this developmental trait, older lamellae are present at deeper depths in the soil sequence. Generally, clay content is greatest near the middle of the soil sequence where lamellae are better developed. But because the wetting front is not perfectly horizontal, clays from the lower lamellae are eventually eroded away. Therefore, clay content is least prevalent near the top and bottom of the sequence (Schaetzl, 2001; Soil Survey Staff, 1999).
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Figure 1-3. Lamellae are prominent in the stratigraphic sequence studied (Photo credit: Lyssa A. Cousineau). Anthropogenic Activity Evidence along the coast including shell middens, stone projectile points, and hearths indicate that a relatively modest number of people lived in and around Los Osos during the Early Holocene (CA State Parks, 1988; Orme, 1990 and 2005). Additionally, radiocarbon dates of Native American middens indicate that the dunes were inhabited by a greater number of people between 4-ka to 2-ka. The Northern Chumash people began to inhabit the region after 4-ka. Their semi-nomadic lifestyle came to an end around 1772 BP, when the Franciscans founded Mission San Luis Obispo de Tolosa (CA State Parks, 1988; Orme, 2005).
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Spanish colonization initiated an agricultural era in which most of the coast (including Montaña de Oro) was heavily grazed by livestock (CA State Parks, 1988; Orme, 2005). During the mid-twentieth century, urbanization and recreational lands curtailed heavy grazing in many areas including the focus of this research. Since urbanization, the dunes have been subjected to several natural and anthropogenic disturbances including military exercises, off-road vehicular traffic, and fire.
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MATERIALS AND METHODS Study Area This study was conducted in Montaña de Oro State Park, located on the central California coast eighteen kilometers northwest of San Luis Obispo in San Luis Obispo County (Figure 2-1; CA State Parks, 1988). Climate San Luis Obispo County soils are in a xeric moisture regime. The Mediterranean climate of the region is characterized by mild temperatures with warm dry summers and cool wet winters, as well as minimal diurnal fluctuations (CA State Parks, 1988; Orme, 1990). The region has an average annual temperature of about 13 to 16° Celsius. Fog occurs frequently along the coast during the summer months. Rainfall averages about 68 cm per year. Precipitation typically occurs during the fall and winter. There are generally forty to sixty days of precipitation per year. Winds are predominantly from the WNW and NW. Vegetation Coastal strand vegetation on the Morro dunes includes ice plant (Carpobrotus chilensis), sea-rocket (Cakile maritima), sand verbena (Abronia latifolia), bush lupine (Lupinus chamissonis), and perennial veldt grass (Ehrharta calycina) (Brady, 1978; CA State Parks, 1988; Lynn E. Moody, PhD, personal communication, 2012). Young terraces are home to Morro manzanita (Arctostaphylos morroensis), buck brush (Ceanothus cuneatus), as well as annual grasses (Moody and Graham, 1995). Older terraces are inhabited by annual shrubs and grasses, poison oak (Toxicodendron diversilobum), California sagebrush (Artemesia californica), and coyote brush (Baccharis pilularis).
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Morro Manzanita and chamise (Adenostoma fasciculatum) comprise most of the vegetation located on the oldest terraces.
Figure 2-1. Oblique aerial view of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Copyright © 2002-2012 Kenneth & Gabrielle Adelman, California Coastal Records Project, www.Californiacoastline.org). The specific site of study is outlined and enlarged. Soils Moody et al. (1994) classified recent Holocene deposits near the study site as mixed, thermic, Argic Xeropsamments. Under the current Keys of Soil Taxonomy, this soil is classified as a mixed, thermic, Lamellic Xeropsamment (NRCS, 2010). South of the Morro Bay barrier beach the dunes are mapped as Dune Land (miscellaneous land area) and Baywood fine sand (sandy, mixed, thermic Entic Haploxerolls), that are composed of eolian deposits. Santa Lucia shaly clay loam (clayey-skeletal, mixed, superactive, thermic Pachic Ultic Haploxerolls) and Arnold loamy sand (mixed, thermic 12
Typic Xeropsamments) are also present. These complexes are composed of residuum from weathered shale and are characterized by steep slopes, seepage and piping features, shallow depth to rock, and unsuitability for construction and engineering (California Soil Resource Lab, 2011; CA State Parks, 1988; NRCS, 2010 and 2011; Soil Survey Division Staff, 1993). Steeper slopes in the area consist of the Lopez-Rock outcrop complex (loamy-skeletal, mixed, superactive, thermic Lithic Ultic Haploxerolls) that support coastal sage scrub and reflect the features of regional soils. Methods Sample Collection The study site is located about 1.5 km north of Hazard Canyon at Montaña de Oro State Park, Los Osos, California. The sampling site was chosen for prominent pedogenic features such as lamellae, and a relative lack of colluvial sediments at the base of the sea cliff (Figure 2-2). The sand deposits lie on top of a modern wave-cut platform. The shoreline angle is covered by colluvial sediments. The sampling protocol was approved by a statistician before collection. Five replicates of each interval were sampled. Samples were collected from the vertical exposure of one dune face by stratified random sampling at 1.0-m vertical intervals (Figure 2-3; Penneck et al., 2008). Forty-five samples in total were collected, with five samples from each 1.0-m vertical interval. A colluvial apron is present up to 1.5m at the base of the dune formation and was not sampled for this study. Two intervals near the top of the dune at 3 to 5 meters depth could not be collected because of inaccessibility. Two samples from each interval were collected to make thin sections, but one of the samples from 0 to 1 meters depth was lost during transport.
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Figure 2-2. View from beach of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Lyssa A. Cousineau). Donovan Hall, who is 1.73m tall, is shown for scale.
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Figure 2-3. Sampling intervals depicted on oblique aerial view of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Copyright © 2002-2012 Kenneth & Gabrielle Adelman, California Coastal Records Project, www.Californiacoastline.org). Laboratory Analyses Particle-size analysis by hydrometer and sieve was conducted following chemical dispersion using 1M sodium hexametaphosphate and physical dispersion for five minutes in an industrial blender (Gee and Bauder, 1986; Kroetsch and Wang, 2008; Sherard et al.,
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1976; Volk, 1937). Electrical conductivity and pH were determined using a 1:1 soil/water paste. Total soil carbon and nitrogen contents were determined using a VarioMax CNS combustion analyzer (Rutherford et al., 2008; Skjemstad and Baldock, 2008). Samples were tested for presence of carbonates with 10% hydrochloric acid; the samples did not contain detectable carbonates. Organic matter was removed by sodium hypochlorite in preparation for two selective dissolution techniques (Courchesne and Turmel, 2008; Soukup et al., 2008). These methods were used to extract pedogenic iron oxides. Ammonium oxalate in the dark extracts poorly crystalline iron oxides (ferrihydrite) from samples (Fey and LeRoux, 1977; Hodges and Zelazny, 1980; Schwertmann, 1964; Shang and Zelazny, 2008). Citrate-bicarbonate-dithionite (CBD) extracts free iron oxides (hematite, goethite, and maghemite) from samples (Jackson et al., 1986; Mehra and Jackson, 1960; Shang and Zelazny, 2008). Pedogenic iron oxides were then quantified from each extractant by flame atomic absorption spectrometry on a SpectrAA (Wright and Stuczynski, 1996). Fifteen thin sections from varying stratigraphic intervals on the dune were analyzed using petrographic microscopy following procedure presented in Vepraskas and Wilson (2008). Sand mineralogy was identified and quantified using polarized light microscopy through grain counts of the thin sections with at least 300 grains per sample (FitzPatrick, 1993; Lynn et al., 2008). Statistical Analyses Numerical data were analyzed by statistical regression in MiniTab. Regression analysis assumes a linear trend and normal residuals with equal variability. Fitted line plots were graphed with four-in-one residual plots to determine fit. P-factors were
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determined from these linear regression analyses. Grouping information was determined by the Tukey method with 95% confidence in conjunction with a general linear model ANOVA. ANOVA assumes normal residuals with equal variability. Data from sampling interval I, with a depth of 5 to 6 meters, were omitted from the regression analyses because those observations were taken on a different day. A table of data for the statistical regressions is presented in Appendix A.
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RESULTS Chemical Features Results of five replicate samples for each stratigraphic interval were averaged together to provide mean data at each 1.0-m vertical interval. Mean electrical conductivity, pH, nitrogen, and total carbon are presented in Table 3-1. Sands from this stratigraphic interval are generally acidic (pH7) (Figure 3-1). The pH is then low between 9 to 11 meters. Total carbon content is greatest at 0 to 1 meters and decreases with depth (Figure 3-2). Regression analysis indicates that total carbon content significantly decreases with depth by exponential regression (0
A Thesis presented to the Faculty of California Polytechnic State University, San Luis Obispo
In Partial Fulfillment of the Requirements for the Degree Master of Science in Agriculture, Specialization in Soil Science
by Lyssa A. Cousineau June 2012
© 2012 Lyssa Anne Cousineau ALL RIGHTS RESERVED
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COMMITTEE MEMBERSHIP
TITLE:
Stratigraphy of Quaternary Dunes by Sand Mineralogy and Pedogenic Features, Los Osos, California
AUTHOR:
Lyssa A. Cousineau
DATE SUBMITTED:
June 2012
COMMITTEE CHAIR:
Dr. Lynn E. Moody, Professor of Natural Resources Management and Environmental Sciences
COMMITTEE MEMBER:
Dr. Antonio F. Garcia, Professor of Geology in the Physics Department
COMMITTEE MEMBER:
Dr. William L. Preston, Professor of Geography
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ABSTRACT Stratigraphy of Quaternary Dunes by Sand Mineralogy and Pedogenic Features, Los Osos, California Lyssa A. Cousineau The goal of this study was to assess mineralogy and pedogenic features of sand dunes in a stratigraphic sequence. The purpose was to determine whether these features significantly differ to reflect age differences with depth within the sequence. This study was conducted in Montaña de Oro State Park, located on the central Californian coast eighteen kilometers northwest of San Luis Obispo in San Luis Obispo County. Samples were collected from the vertical exposure of one dune face by stratified random sampling at 1.0-m vertical intervals. Particle size distribution was determined through particle-size analysis by hydrometer and sieve. Electrical conductivity and pH were determined using a 1:1 soil/water paste. Total soil carbon and nitrogen contents were determined by combustion. Pedogenic iron oxides were extracted by ammonium oxalate in the dark and citrate-bicarbonate-dithionite, and then quantified by flame atomic absorption spectrometry. Sand mineralogy of fifteen thin sections was analyzed by polarized light microscopy. Grain counts quantified the sand mineralogy of the thin sections. Total carbon significantly decreases with soil depth and age reflecting modern development of soil at 0 to 1 meters within the stratigraphic sequence. Certain morphologic and mineralogic features, including an increase in nitrogen content and the presence of fossilized fungal hyphae, suggest that a buried A horizon may be preserved 9 to 10 meters below the crest of the modern dune complex. Using relative dates compiled from previous research, it was determined that the soil at 9 to 10 meters depth was developed 15-ka to 30-ka after sand deposition during a eustatic sea level lowstand. The presence of fossils in general suggests that the ancient soil was rapidly covered.
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ACKNOWLEDGEMENTS There are so many individuals to thank for this accomplishment, I cannot mention them all. Therefore, I provide this broad (and sincere!) statement. To my colleagues from the Natural Resources Management and Environmental Sciences Department as well as my family and friends spread throughout North America, thank you for teaching me, encouraging me, and allowing me to laugh at myself when the going got rough. I extend sincerest gratitude to my committee chair, Dr. Lynn Moody. Thank you for your wisdom, guidance and continual support. You are an inspiration and a joy to be around, Lynn, and I would not have grown by leaps and bounds in two years without your counsel. You will be missed in the soils profession when you retire this year. I would also like to thank my graduate committee, Dr. William Preston and Dr. Antonio Garcia. Thank you for your manuscript edits, insights, and humor inside and outside of committee meetings. Laboratory assistance was absolutely essential to my research. Technician Craig Stubler, your expertise was invaluable to my laboratory procedures and analysis. Thank you for your dedication in helping me with my thesis. You went above and beyond what I asked for, and without hesitation. All departments should be so blessed to have a technician such as you. Adrian Gallo and Scott Pensky, my undergraduate research assistants, thank you for your long hours in the lab. You kept the lab lively when I needed it most, and provided me with a fresh outlook on my research. Thomas Witman, Craig’s lab assistant, surprised me by volunteering his time in the lab working on my project. Without you guys, I would not have finished in such a timely manner. I hope this experience has been as great a learning tool for you as it has been for me. I look forward to hearing about your adventures in soil science when you begin your careers in the near future. Dr. Tryg Lundquist, from the Civil and Environmental Engineering Department at Cal Poly San Luis Obispo, thank you for letting me use your centrifuge for sample preparation. We ended up completely wearing out a relay on your thirty-year-old machine, and I had to completely redesign my procedure because the centrifuge is now unavailable indefinitely. Whoops. National Petrographic Service, Inc. prepared thin sections with a partial grant from the Natural Resources Management and Environmental Sciences Department at Cal Poly San Luis Obispo. To Lisa Wallravin, Melanie Gutierrez and Becky Powell: You work tirelessly behind-the-scenes to make sure all the coursework, paperwork, and formatting is correct. Without your dedication and hard work, none of the Master’s students would ever make it out of Cal Poly! Jacqueline Tilligkeit, Dr. Thomas J. Rice, Lynette Niebrugge, Leslie Wilson, Shelby Delfino, and Brittany Piarulli, thanks for all of your encouragement and support in completing this thesis. I am particularly grateful to Donovan Hall, who not only assisted me with sample collection, but also was my chauffer, encouragement, chef, best friend, shoulder to cry on, and (amazingly) my occasional lab assistant. When I started this thesis, I had yet to meet you; now I cannot imagine my life without you. Last but not least, I would like to thank my parents and the Lord; without you, I would have never made it this far.
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TABLE OF CONTENTS Page LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix INTRODUCTION .............................................................................................................. 1 Geologic Background ............................................................................................. 2 Marine Terraces ...................................................................................................... 4 Relative Ages .............................................................................................. 5 Basal Dune Chronology .............................................................................. 6 Sand Dune Development ........................................................................................ 7 Lamellae ...................................................................................................... 8 Anthropogenic Activity .......................................................................................... 9 MATERIALS AND METHODS ...................................................................................... 11 Study Area ............................................................................................................ 11 Climate ...................................................................................................... 11 Vegetation ................................................................................................. 11 Soils........................................................................................................... 12 Methods................................................................................................................. 13 Sample Collection ..................................................................................... 13 Laboratory Analyses ................................................................................. 15
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Statistical Analyses ................................................................................... 16 RESULTS ......................................................................................................................... 18 Chemical Features ................................................................................................. 18 Texture .................................................................................................................. 22 Particle Size Distribution .......................................................................... 22 Roundness and Sorting ............................................................................. 24 Mineralogy and Micromorphology ....................................................................... 25 Selective Dissolution ............................................................................................ 31 DISCUSSION ................................................................................................................... 36 Modern Soil Development .................................................................................... 36 Lamellae .................................................................................................... 36 Pedogenic Iron Oxides .......................................................................................... 37 Paleosol ................................................................................................................. 37 Relative Dating of Paleosol .................................................................................. 39 CONCLUSIONS............................................................................................................... 41 LIST OF REFERENCES .................................................................................................. 43 APPENDIX ....................................................................................................................... 49 A.
Table of Results for Regression Analyses .............................................. 50
B.
Plates of Thin Section Features ............................................................... 53
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LIST OF TABLES Page Table 1-1. The four major coastal dune phases of stabilization and their maximum ages in the Morro Dune Complex (Orme, 1990). ..............................................7 Table 3-1. Selected chemical features of stratigraphic sequence. .....................................19 Table 3-2. Particle size distribution of sand grains. ...........................................................23 Table 3-3. Prominent sorting and roundness of sand grains. Roundness not determined at 5 to 6 meters because thin sections were not produced for that stratigraphic interval. ...........................................................................25 Table 3-4. Sand mineralogy of thin sections. All samples were averaged except for 0 to 1 meters, which is a single sample set because of sample loss. ..........26 Table 3-5. Root counts in thin sections. Total root count includes roots and root channels discovered independent of the grain count. ......................................29 Table 3-6. Selective dissolution chemical data for stratigraphic sequence. ......................33 Table 3-7. Grouping information using the Tukey method with 95% confidence for total pedogenic iron oxides (Fed) and poorly crystalline iron oxides (Feo)..................................................................................................................34
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LIST OF FIGURES Page Figure 1-1. Late Quaternary sand dunes of the Morro Dune Complex in Estero Bay. Active dunes are adjacent to the coast, and younger parabolic dunes reside east of the active dunes. Morro barrier tip circled in red. Figure adopted from Orme, 1990. ....................................................................3 Figure 1-2. Timeline of geologic, glacial, and historic events pertinent to the central Californian coast. ..................................................................................5 Figure 1-3. Lamellae are prominent in the stratigraphic sequence studied (Photo credit: Lyssa A. Cousineau). ............................................................................9 Figure 2-1. Oblique aerial view of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Copyright © 20022012 Kenneth & Gabrielle Adelman, California Coastal Records Project, www.Californiacoastline.org). The specific site of study is outlined and enlarged. ....................................................................................12 Figure 2-2. View from beach of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Lyssa A. Cousineau). Donovan Hall, who is 1.73m tall, is shown for scale. ....................................14 Figure 2-3. Sampling intervals depicted on oblique aerial view of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Copyright © 2002-2012 Kenneth & Gabrielle Adelman, California Coastal Records Project, www.Californiacoastline.org). ..............15
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Figure 3-1. Average pH of stratigraphic sequence. Depth is in meters and error bars display standard error. ............................................................................20 Figure 3-2. Average total carbon of stratigraphic sequence. The trend line displays exponential regression. Depth is in meters and error bars display standard error. .................................................................................................20 Figure 3-3. Average nitrogen of stratigraphic sequence. Depth is in meters and error bars display standard error. ....................................................................21 Figure 3-4. Electrical conductivity of stratigraphic sequence. Depth is in meters and error bars display standard error. .............................................................21 Figure 3-5. Sand distribution as determined by particle size analysis in stratigraphic sequence. Depth is in meters and error bars display standard error. .................................................................................................23 Figure 3-6. Silt and clay distribution as determined by particle size analysis in stratigraphic sequence. Depth is in meters and error bars display standard error. .................................................................................................24 Figure 3-7. Sand mineralogy of stratigraphic sequence. Depth is in meters, error bars display standard error, and x-axis is in percent. .....................................27 Figure 3-8. Selected sand mineralogy of quartz in stratigraphic sequence. Depth is in meters, error bars display standard error, and x-axis is in percent. ............27 Figure 3-9. Selected sand mineralogy of plagioclase in stratigraphic sequence. Depth is in meters, error bars display standard error, and x-axis is in percent. ...........................................................................................................28
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Figure 3-10. Quartz to plagioclase ratio in stratigraphic sequence. Depth is in meters and error bars display standard error. .................................................28 Figure 3-11. Selected sand mineralogy of minor grains in stratigraphic sequence. Depth is in meters, error bars display standard error, and x-axis is in percent. Quartz and plagioclase omitted from this figure to better depict concentrations of minor grains. ...........................................................29 Figure 3-12. Cross section of root covered by mycorrhizal sheath (FitzPatrick, 1993) located 0 to 1 meters depth under cross-polars at 40X magnification (Photomicrograph credit: Lyssa A. Cousineau). .....................30 Figure 3-13. Filamentous, branching structures of fungal hyphae between grains located 9 to 10 meters depth under plane polarized light at 40X magnification (Photomicrograph credits: Lyssa A. Cousineau and Adrian Gallo). .................................................................................................31 Figure 3-14. Poorly crystalline iron oxides (Feo) of stratigraphic sequence. Depth is in meters and error bars display standard error. .........................................33 Figure 3-15. Total pedogenic iron oxides (Fed) of stratigraphic sequence. Depth is in meters and error bars display standard error. .............................................34 Figure 3-16. Ratio of poorly crystalline iron oxides (Feo) to total pedogenic iron oxides (Fed) of stratigraphic sequence. Depth is in meters and error bars display standard error. ............................................................................35
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INTRODUCTION Dune geomorphology and coastal dune research are important because coastal dunes are dynamic. Coastal dunes experience periods of stabilization and inconstancy, and are subject to frequent and rapid changes due to sea level flux, shifts in vegetation, and anthropogenic activity (Carter et al., 1990; Orme, 1990 and 2005). These changes are compounded by modern global climate change, which is also altering coastal environments on a global scale. A lack of complete understanding of coastal dunes during this period of rapidly evolving landscapes may lead to the loss of these habitats for future generations. Preservation is crucial for archaeological research. The value of archaeological sites is dependent on accurate provenance, or the age and location of artifacts. If archaeologists understand dune development and age, they will be afforded with a better opportunity to determine artifact provenance. Shell middens and archaeological sites created by the Chumash at Montaña de Oro State Park (CA State Parks, 1988; Orme, 1990 and 2005) are often associated to the dunes. Understanding of Chumash life ways will be enhanced by this research. The general public enjoys the central coast of California because of good weather, opportunities for recreational activities, and a plethora of native fauna and flora. These qualities have also been valuable to the Chumash for thousands of years. It is our job to preserve this heritage. Several studies have analyzed the development of sand dunes, sandy soils, and underlying marine terraces (Aniku and Singer, 1990; Graham and O’Geen, 2010; Johnson et al., 2008; Little et al., 1978; Macphail and McAvoy, 2008; Miles and Franzmeier, 1981; Moody and Graham, 1995 and 1997; Reheis et al., 2005; Sauer et al.,
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2010; Tsai et al., 2007; Tsai et al., 2010; Wagner et al., 2007), but characteristics of coastal dunes worldwide are still being compiled. This study analyzes stratigraphy of a select dune complex located within Montaña de Oro State Park. The goal of this study is to assess mineralogy and pedogenic features of sand dunes in a stratigraphic interval. The purpose is to determine whether these features significantly differ to reflect age differences with depth. Geologic Background Tectonic activity, sea level changes, and anthropogenic events are paramount to the evolution of the central California coast (Keller, 1992; Orme, 1990 and 2005). Montaña de Oro State Park is at the northwest end of the San Luis Range. This range, along with the Santa Lucia and Casmalia Hills Coastal Ranges developed over the last 5 to 3.5 million years due to folding and faulting along the Pacific and North American plates (Page et al., 1998). More recently, the Morro Bay estuary began to form approximately 5-ka (Page et al., 1998). The current modern-day landscape of the Morro Bay estuary developed when an oceanic breach flooded a structurally unsound trough (Figure 1-1; CA State Parks, 1988; Orme, 1990 and 2005). Orme (1990) named the dune deposits in this area as the Morro Dune Complex. The Morro Dune Complex has been the focus of study since the turn of the twentieth century. Marine terraces between Morro Bay and Santa Maria Valley were first noted by Fairbanks (1904). Fairbanks classified the rock sequence of Montaña de Oro as Monterey Shale (i.e., Monterey Formation). But this delineation was overturned by Hall (1973) who reclassified the shale, siltstone, and claystone as part of the Miguelito
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Member of the Pismo Formation (Keller, 1992; Orme, 1990). Later studies conducted by Pacific Gas and Electric Company (1973, 1988) and Cleveland (1978) followed Hall’s classification.
Figure 1-1. Late Quaternary sand dunes of the Morro Dune Complex in Estero Bay. Active dunes are adjacent to the coast, and younger parabolic dunes reside east of the active dunes. Morro barrier tip circled in red. Figure adopted from Orme, 1990. 3
Marine Terraces Marine terraces develop due to oscillating eustatic sea level highstands and lowstands. During an interglacial period, when less water is bound in glacial ice, sea levels rise. Periods of global sea level rise are known as transgressions, and periods of global sea level fall are termed regressions. Wave erosion from elevated sea level cuts a bedrock bench at the shoreline and thus creates a sea cliff that adjoins perpendicular to a modern wave-cut platform at the shoreline angle. These features are later uplifted by tectonic forces. The uplifted wave-cut platform is now a called a strath and the former (uplifted) sea cliff is now termed a riser. As the shoreline ridge and platform continues to uplift and waves from the modern sea level cut into the bedrock bench, additional straths and risers are formed and a staircase of shoreline platforms emerges. The top of the staircase is inhabited by the oldest shoreline platforms; the straths and risers become progressively older inland and with increasing elevation. The modern wave-cut platform overlain by the current coastal shore is generally indicative of the most recent coastal activity. However, sea level regressions can create platforms which later exist under water during a eustatic sea level highstand or interglacial period. Orme (1990) identified intermittent uplift of shoreline ridges in the Morro Dune Complex since about 100-ka (Figure 1-2). The current average uplift rate for marine terraces located between Islay Creek and Hazard Canyon in Montaña de Oro State Park, which is very close to the study site, is approximately 0.24 m/ka (Hanson et al., 1994). During eustatic sea level lowstands, sediments previously below sea level become subject to eolian processes. Winds dominantly from the west (CA State Parks, 1988; Orme, 1990) transport sand dunes inland to cover the wave-cut platforms. These dunes
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are migratory and are constantly being reworked by the winds, but coastal shrubs and vegetation create stationary areas within otherwise mobile modern sand dunes.
Figure 1-2. Timeline of geologic, glacial, and historic events pertinent to the central Californian coast. 1 Relative Ages Dates of the marine terraces at Morro Bay and Montaña de Oro State Park have been disputed over the years. Using a combination of amino acid racemization, uraniumseries dating from coral and vertebrate bone samples, invertebrate faunal assemblages, 1
(Ogg, 2010) 2(Muhs, 2012) 3(Gibbard and Kolfschoten, 2004) 4(Orme, 1990) 5(CA Dept. of Water Resources, 2002) 6(Moody and Graham, 1995) 7(Jack Meyer, Far Western Anthropological Research Group, Inc., personal communication, 2012) 8(Hanson et al., 1994) 9(Bischoff and Rosenbauer, 1981)
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and comparisons of terrace elevation with altitudes of previously-dated terraces, Hanson et al. (1994) determined that an array of twelve elevated, essentially flat-lying marine terraces exist in the San Luis Range between Morro Bay and the northern boundary of Santa Maria Valley. According to this study, the youngest and lowest two terraces of the dozen correlate consecutively with sea-level transgressions at 80-ka and 120-ka. Hanson et al. (1994) concluded that a thin terrace dating to the 105-ka transgression was eroded and subsequently not preserved. A concurrent study by Moody and Graham (1995) determined that the lowest terrace dates to the 120-ka interglacial, and that overlying sands were first deposited during the Pleistocene (12-ka to 27-ka or 48-ka) and reworked later during the Holocene (1-ka). Basal Dune Chronology Modern beaches and dune fields, which date from the late Pleistocene to the early Holocene, overlie the marine terraces in Morro Bay and at Montaña de Oro State Park (Hanson et al., 1994; Orme, 1990 and 2005). Sands of these beaches and dune fields were deposited on the San Luis Range during the last eustatic sea level lowstand at about 15-ka (CA State Parks, 1988; Orme, 1990 and 2005). Dates from Gibson (1981) and Orme (1990) indicate that the surface dune deposits located 2.3 km south of the Morro barrier tip (see Figure 1-1) date between 3568 and 3830 BP (before present) (Jack Meyer from Far Western Anthropological Research Group, Inc., personal communication, 2012). The study site is located relatively close to the surface dune deposits dated. Therefore, surface dune deposits of the study site likely correlate with these ages. Additional radiocarbon
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dating of buried soils indicates that dunes which were formed during the last drop in sea level have since partially eroded (Orme, 1990). Orme (1990) defined four major phases of dune stabilization in Morro Bay (Table 1). His work suggests that the modern dunes of the Morro Dune Complex are experiencing a period of instability, and that dune erosion is marked and rapid in the region today. It is likely that the basal layer of the study site corresponds with the youngest paleodunes which were deposited on the San Luis Range between 15-ka to 30ka (CA State Parks, 1988; Orme, 1990 and 2005). Table 1-1. The four major coastal dune phases of stabilization and their maximum ages in the Morro Dune Complex (Orme, 1990). Phase
Expression
Maximum age (uncalibrated)
Holocene III
Active dunes
< 200 BP
Holocene II
Younger parabolic and lobate dunes
< 1,730 BP
Holocene I
Older parabolic dunes
≤ 4,160 BP
Late Pleistocene
Youngest paleodunes
< 27,000 BP
Sand Dune Development Coastal watersheds brought inland sediment to the coasts by flood events, which were then reworked by waves, winds, and currents to form the modern sand dunes found along the Pacific coast. The collection of sediment on these coasts was most prevalent during the wetter climate of the Pleistocene. However, tectonic deformation of Los Osos Valley toward the end of the Pleistocene limited sediment delivery (Orme, 2005). Dunes are influenced by beach profile characteristics, wind regimes, and sediment grain size distribution (Carter et al., 1990). Sand deposits, which make up coastal dunes, are positioned in response to obstructions including vegetation and anthropogenic 7
obstacles such as jetties and buildings. The wave-cut platforms at Montaña de Oro State Park are overlain with a thin (1 to 2 m) deposit of gravel and marine sand, and a thick (up to 30 m) deposit of eolian sand, alluvium, and colluvium (Hanson et al., 1994; Moody and Graham, 1997; Orme, 1990). Lamellae The dune complex for this study contains an extensive array of lamellae throughout the soil section (Figure 1-3). The Keys to Soil Taxonomy, Eleventh Edition (NRCS, 2010) defines lamellae as the following: A lamella is an illuvial horizon less than 7.5 cm thick formed in unconsolidated regolith more than 50 cm thick. Each lamella contains an accumulation of oriented silicate clay on or bridging the sand and silt grains (and rock fragments if any are present). Each lamella is required to have more silicate clay than the overlying eluvial horizon. In general, lamellae number, color, and thickness increase with pedogenic development (Schaetzl, 2001). Specifically, to some threshold depth below which clay illuviation is negligible, the process of lamellae development increases with depth and age of a soil sequence. This is because lamellae migrate downward in a soil sequence. The clay content moves from upper to lower lamellae during development (Soil Survey Staff, 1999). Because of this developmental trait, older lamellae are present at deeper depths in the soil sequence. Generally, clay content is greatest near the middle of the soil sequence where lamellae are better developed. But because the wetting front is not perfectly horizontal, clays from the lower lamellae are eventually eroded away. Therefore, clay content is least prevalent near the top and bottom of the sequence (Schaetzl, 2001; Soil Survey Staff, 1999).
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Figure 1-3. Lamellae are prominent in the stratigraphic sequence studied (Photo credit: Lyssa A. Cousineau). Anthropogenic Activity Evidence along the coast including shell middens, stone projectile points, and hearths indicate that a relatively modest number of people lived in and around Los Osos during the Early Holocene (CA State Parks, 1988; Orme, 1990 and 2005). Additionally, radiocarbon dates of Native American middens indicate that the dunes were inhabited by a greater number of people between 4-ka to 2-ka. The Northern Chumash people began to inhabit the region after 4-ka. Their semi-nomadic lifestyle came to an end around 1772 BP, when the Franciscans founded Mission San Luis Obispo de Tolosa (CA State Parks, 1988; Orme, 2005).
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Spanish colonization initiated an agricultural era in which most of the coast (including Montaña de Oro) was heavily grazed by livestock (CA State Parks, 1988; Orme, 2005). During the mid-twentieth century, urbanization and recreational lands curtailed heavy grazing in many areas including the focus of this research. Since urbanization, the dunes have been subjected to several natural and anthropogenic disturbances including military exercises, off-road vehicular traffic, and fire.
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MATERIALS AND METHODS Study Area This study was conducted in Montaña de Oro State Park, located on the central California coast eighteen kilometers northwest of San Luis Obispo in San Luis Obispo County (Figure 2-1; CA State Parks, 1988). Climate San Luis Obispo County soils are in a xeric moisture regime. The Mediterranean climate of the region is characterized by mild temperatures with warm dry summers and cool wet winters, as well as minimal diurnal fluctuations (CA State Parks, 1988; Orme, 1990). The region has an average annual temperature of about 13 to 16° Celsius. Fog occurs frequently along the coast during the summer months. Rainfall averages about 68 cm per year. Precipitation typically occurs during the fall and winter. There are generally forty to sixty days of precipitation per year. Winds are predominantly from the WNW and NW. Vegetation Coastal strand vegetation on the Morro dunes includes ice plant (Carpobrotus chilensis), sea-rocket (Cakile maritima), sand verbena (Abronia latifolia), bush lupine (Lupinus chamissonis), and perennial veldt grass (Ehrharta calycina) (Brady, 1978; CA State Parks, 1988; Lynn E. Moody, PhD, personal communication, 2012). Young terraces are home to Morro manzanita (Arctostaphylos morroensis), buck brush (Ceanothus cuneatus), as well as annual grasses (Moody and Graham, 1995). Older terraces are inhabited by annual shrubs and grasses, poison oak (Toxicodendron diversilobum), California sagebrush (Artemesia californica), and coyote brush (Baccharis pilularis).
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Morro Manzanita and chamise (Adenostoma fasciculatum) comprise most of the vegetation located on the oldest terraces.
Figure 2-1. Oblique aerial view of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Copyright © 2002-2012 Kenneth & Gabrielle Adelman, California Coastal Records Project, www.Californiacoastline.org). The specific site of study is outlined and enlarged. Soils Moody et al. (1994) classified recent Holocene deposits near the study site as mixed, thermic, Argic Xeropsamments. Under the current Keys of Soil Taxonomy, this soil is classified as a mixed, thermic, Lamellic Xeropsamment (NRCS, 2010). South of the Morro Bay barrier beach the dunes are mapped as Dune Land (miscellaneous land area) and Baywood fine sand (sandy, mixed, thermic Entic Haploxerolls), that are composed of eolian deposits. Santa Lucia shaly clay loam (clayey-skeletal, mixed, superactive, thermic Pachic Ultic Haploxerolls) and Arnold loamy sand (mixed, thermic 12
Typic Xeropsamments) are also present. These complexes are composed of residuum from weathered shale and are characterized by steep slopes, seepage and piping features, shallow depth to rock, and unsuitability for construction and engineering (California Soil Resource Lab, 2011; CA State Parks, 1988; NRCS, 2010 and 2011; Soil Survey Division Staff, 1993). Steeper slopes in the area consist of the Lopez-Rock outcrop complex (loamy-skeletal, mixed, superactive, thermic Lithic Ultic Haploxerolls) that support coastal sage scrub and reflect the features of regional soils. Methods Sample Collection The study site is located about 1.5 km north of Hazard Canyon at Montaña de Oro State Park, Los Osos, California. The sampling site was chosen for prominent pedogenic features such as lamellae, and a relative lack of colluvial sediments at the base of the sea cliff (Figure 2-2). The sand deposits lie on top of a modern wave-cut platform. The shoreline angle is covered by colluvial sediments. The sampling protocol was approved by a statistician before collection. Five replicates of each interval were sampled. Samples were collected from the vertical exposure of one dune face by stratified random sampling at 1.0-m vertical intervals (Figure 2-3; Penneck et al., 2008). Forty-five samples in total were collected, with five samples from each 1.0-m vertical interval. A colluvial apron is present up to 1.5m at the base of the dune formation and was not sampled for this study. Two intervals near the top of the dune at 3 to 5 meters depth could not be collected because of inaccessibility. Two samples from each interval were collected to make thin sections, but one of the samples from 0 to 1 meters depth was lost during transport.
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Figure 2-2. View from beach of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Lyssa A. Cousineau). Donovan Hall, who is 1.73m tall, is shown for scale.
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Figure 2-3. Sampling intervals depicted on oblique aerial view of marine terrace study area at Montaña de Oro State Park, Los Osos, California (Photo credit: Copyright © 2002-2012 Kenneth & Gabrielle Adelman, California Coastal Records Project, www.Californiacoastline.org). Laboratory Analyses Particle-size analysis by hydrometer and sieve was conducted following chemical dispersion using 1M sodium hexametaphosphate and physical dispersion for five minutes in an industrial blender (Gee and Bauder, 1986; Kroetsch and Wang, 2008; Sherard et al.,
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1976; Volk, 1937). Electrical conductivity and pH were determined using a 1:1 soil/water paste. Total soil carbon and nitrogen contents were determined using a VarioMax CNS combustion analyzer (Rutherford et al., 2008; Skjemstad and Baldock, 2008). Samples were tested for presence of carbonates with 10% hydrochloric acid; the samples did not contain detectable carbonates. Organic matter was removed by sodium hypochlorite in preparation for two selective dissolution techniques (Courchesne and Turmel, 2008; Soukup et al., 2008). These methods were used to extract pedogenic iron oxides. Ammonium oxalate in the dark extracts poorly crystalline iron oxides (ferrihydrite) from samples (Fey and LeRoux, 1977; Hodges and Zelazny, 1980; Schwertmann, 1964; Shang and Zelazny, 2008). Citrate-bicarbonate-dithionite (CBD) extracts free iron oxides (hematite, goethite, and maghemite) from samples (Jackson et al., 1986; Mehra and Jackson, 1960; Shang and Zelazny, 2008). Pedogenic iron oxides were then quantified from each extractant by flame atomic absorption spectrometry on a SpectrAA (Wright and Stuczynski, 1996). Fifteen thin sections from varying stratigraphic intervals on the dune were analyzed using petrographic microscopy following procedure presented in Vepraskas and Wilson (2008). Sand mineralogy was identified and quantified using polarized light microscopy through grain counts of the thin sections with at least 300 grains per sample (FitzPatrick, 1993; Lynn et al., 2008). Statistical Analyses Numerical data were analyzed by statistical regression in MiniTab. Regression analysis assumes a linear trend and normal residuals with equal variability. Fitted line plots were graphed with four-in-one residual plots to determine fit. P-factors were
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determined from these linear regression analyses. Grouping information was determined by the Tukey method with 95% confidence in conjunction with a general linear model ANOVA. ANOVA assumes normal residuals with equal variability. Data from sampling interval I, with a depth of 5 to 6 meters, were omitted from the regression analyses because those observations were taken on a different day. A table of data for the statistical regressions is presented in Appendix A.
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RESULTS Chemical Features Results of five replicate samples for each stratigraphic interval were averaged together to provide mean data at each 1.0-m vertical interval. Mean electrical conductivity, pH, nitrogen, and total carbon are presented in Table 3-1. Sands from this stratigraphic interval are generally acidic (pH7) (Figure 3-1). The pH is then low between 9 to 11 meters. Total carbon content is greatest at 0 to 1 meters and decreases with depth (Figure 3-2). Regression analysis indicates that total carbon content significantly decreases with depth by exponential regression (0
